A reference says, BECK AND CALL -- "Immediately available...A 'beck' is a silent signal, such as a nod of the head or a motion with the forefinger. The sense is apparent in the Earl of Worcester's Iulius Cesars Commentaryes : 'It should be ready at a beck.' In summoning a servant one might have to resort to a 'call' as well as a 'beck' if the servant did not see the beck or failed to respond to it." From "The Dictionary of Cliches" by James Rogers (Wings Books, Originally New York: Facts on File Publications, 1985).